| The Blended-wing-body underwater glider(BWBUG)is developed as a new concept of underwater glider.Comparing to traditional underwater glider,the BWBUG has advantages in higher gliding ratio and capacity to carry more payload.As a tailless configuration,the existing BWBUGs share shortness in lateral stability,which will result in yaw and sway motion when encountering turbulence.In this case,the BWBUG cannot sail following a pre-arranged route.To solve the problem,the vertical tail and the winglet,as two types of vertical stabilizer,are taken into consideration.The configuration design is accomplished while the gliding performance of the BWBUG is investigated.The main contribution of this paper can be summarized as follows:(1)A parametric model for BWBUG including the vertical tail,the winglets and the main body is established by combining the NURBS curve conception,the CST parametric model of the foil.Then,the whole procedure is integrated and the 3D configuration model of BWBUG can be generated automatically by using the API interface supported by 3D modeling software.(2)The computational fluid dynamics model is built to obtain the hydrodynamic parameter of the BWBUG.Besides,the results from an experimental study is selected as a reference.Comparison between the experimental study and the results of the computational fluid model shows a satisfied accordance,revealing that the results from computational fluid model is reliable and accurate.Then,the computational fluid model is applied through this paper.The positional hydrodynamic coefficient,the rotational hydrodynamic coefficient and the added mass coefficient of two BWBUGs(one with vertical stabilizer and the other one without)is calculated.Effect of the vertical stabilizer has on hydrodynamic performance is investigated.Besides,an efficiency mesh generation strategy is introduced which can reduce the time consumption of the mesh generation work.The efficient to perform the hydrodynamic analysis has been improved as a result.(3)A model to describe the motion of BWBUG is established.The difference of trajectories between tailless configuration and sample with tails are compared,among which the profiling trajectory,lateral turbulence induced trajectory,and the over-depth as well as over shallow trajectory are considered.Considering that the variation of depth can be large for BWBUG,the buoyancy changing model is established,in which the variation of density of seawater and the deformation of the floating material are taken into account.The influence of the buoyancy changing model has on trajectory is discussed.As a result,the lift-to-drag ratio and the restoring yaw moment are selected as two objectives in following optimization works.(4)An optimization model for vertical stabilizer of BWBUG is established.The OLHS sampling method,Kriging surrogated method,NSGA-Ⅱ multi-objective-optimization algorithm and the new-proposed MAXHVEI supplementary sampling method are applied and integrated into a fully-automatically optimization frame work.Higher lift-to-drag ratio and larger restoring yaw moment coefficient are set as optimization objectives.Taking the tailless BWBUG as a baseline,the optimized pareto fronts is ideal one within which the optimal liftto-drag ratio is improved by 7% while the restoring yaw moment is increased by 223%.(5)Based on the optimization results,the gliding performance of three optimal BWBUG samples are analyzed and compared with each other and the initial tailless sample.Based on the gliding performance analyzing,the three optimal BWBUG samples are able to recover the initial heading direction,when encountering lateral turbulence.However,for the three optimal BWBUG samples,the lateral turbulence will result in lateral displacement,which is proportional to the intensity and duration of the turbulence.In summary,the research and development work of this paper can be adopted to form indepth understanding of BWBUG.The automatic framework and mathematical model proposed in this paper can be applied to reduce the time consumption when designing a BWBUG.Also,the concept of this paper can be adopted as a reference to solve other practical problems. |
